1. Field of Invention
This invention relates, in one aspect, to improvements in voltage regulator circuits and methods for operating same, and, in another aspect, to improvements in mass data storage devices, circuits, and methods, and more particularly to improvements in mass data storage devices, or the like, which include voltage regulator circuits, and methods for using and operating same.
2. Relevant Background
Applications for switched power supplies are manifold. Switched power supplies operate by alternately switching a current onto and away from a path that includes an inductor and a capacitor. The capacitor is connected to one end of the inductor, and sinks and sources the current therein so that as the current is switched, the capacitor maintains the voltage on the node to which it is connected. By controlling the switching time during which current is supplied to the capacitor, the voltage can be regulated to maintain a desired value within a quiescent operating range.
However if load variations disturb the current flow, charge on the capacitor is changed from its quiescent operating range. As a result, it may take an undesirably large amount of time for the power supply to restore the charge on the capacitor to within its quiescent range, and, consequently, to return the power supply to an operation within its quiescent output voltage range.
In the context of a mass data storage device, which is one of many environments in which the power supply and method of the invention may be employed, for example, a magneto-resistive (MR) data transducer or head may be used. The head may be biased by a biasing circuit that maintains a normal or quiescent current in the head (or a normal or quiescent voltage across the head). Such MR heads change resistance when they are moved through changing magnetic fields. As a result, as data, which is magnetically recorded on a magnetic media such as a spinning disk or the like, passes the MR head, the changes in resistance in the head can be detected and decoded to retrieve the data.
However, certain events, such as thermal asperities, may occur that cause large, abnormal transients in the resistance of the MR head. Sometimes, in fact, the MR head may actually undesirably contact a defect in the magnetic media, which may rapidly heat the MR head, and drastically change its resistance. This results in a rapid demand for current from the power supply to the head biasing circuit. On the other hand, sometimes the flight height of the head is significantly increased, such as if a dip were to occur in the magnetic disk above which the head flies. In this case, the head is unexpectedly cooled. This abnormally increases the resistance of the head, and reduces the demands on the power supply to the biasing circuit.
Also, when the circuit performs a read or write operation, the current demands of the DSP of the circuit are changed. The read operation in particular causes the DSP to perform a large amount of data processing. This large increase in processing requires that a large amount of current be supplied.
In either case, with regard to the power supply circuit, rapid changes occur to the charge on the output capacitor, which must be restored to within the quiescent range before the data can again be reliably detected. This restoration takes some time, depending on the size of the capacitor and inductor, and in the meantime, the data cannot be reliably detected.
What is needed, therefore, is a circuit and method for rapidly bringing the output voltage of a switched power supply to within its quiescent operating range after a disturbance. In the context of a mass data storage device, what is needed is a switched power supply of the type described that can rapidly reestablish its quiescent operating range after a disturbance to reduce the amount of time that data cannot be reliably detected.
In light of the above, therefore, it is an object of the invention to provide an improved voltage regulating power supply circuit and method for operating same.
It is another object of the invention to provide a voltage regulating power supply circuit of the type described and method for rapidly bringing the output voltage thereof to within its quiescent operating range after a disturbance.
It is another object of the invention to provide a mass data storage device that uses a voltage regulating power supply circuit of the type described that can rapidly reestablish its quiescent operating range after a disturbance to the data transducer to increase the amount of time that data can be reliably detected.
It is an advantage of the invention that the size of the capacitor used in a switched power supply can be reduced due to the capability of the supply circuit to rapidly recover from transients that pull the output voltage from a quiescent operating range.
It is another advantage of the invention that the circuit and method provide for duty cycle boost or reduction while a feedback loop is still in control of the output, and that this is performed while still keeping the fundamental switching frequency.
These and other objects, features, and advantages will become apparent to those skilled in the art from the following detailed description when read in conjunction with the accompanying drawing and appended claims.
According to a broad aspect of the invention, a switched power supply is presented. The supply has a switched circuit for producing an output voltage, and a circuit for generating pulse width modulated control pulses to control on and off times of the switched circuit to control a magnitude of the output voltage.
According to another broad aspect of the invention, a switched power supply is presented. The supply has a circuit for generating pulse width modulated control pulses to control its output voltage. A first comparator is connected to receive the output voltage on one input and a first reference voltage on another input. When the output voltage exceeds the first reference voltage, the output of the first comparator changes state. A second comparator is connected to receive the output voltage on one input and a second reference voltage on another input. When the second reference voltage exceeds the output voltage, the output of the second comparator changes state. A circuit is then provided changing the pulse width modulated pulses to first or second width limits in response to respective changes of the output states of the first and second comparators.
The circuit for generating pulse width modulated control pulses may include a comparator connected to receive a signal indicating an output voltage of the supply on one input, and a ramp wave signal from a ramp wave generator on another input. An output of the comparator is a signal containing a time width proportional to the output voltage of the supply.
According to yet another broad aspect of the invention, a method is provided for operating a switched power supply. The method includes generating pulse width modulated control pulses to control on and off times of current switches in the supply, and modifying a width of the pulse width modulated control pulses to control a magnitude of the output voltage of the supply. The method also includes, in another aspect, changing a width of the pulse width modulated pulses to a first or a second width limit in response to respective changes of the output voltage beyond first and second predetermined values.
According to still another broad aspect of the invention, a mass data storage device is presented. The mass data storage device includes a switched power supply that provides power to at least one element of the device. The supply includes a switched circuit for producing an output voltage, and a circuit for generating pulse width modulated control pulses to control on and off times of the switching elements to control a magnitude of the output voltage. The device may also include a circuit for changing a width of the pulse width modulated pulses to first or second width limits in response to respective changes of the output voltage beyond first and second predetermined values.